1. Field of the Invention
The present invention relates to a transmission rate control method for controlling transmission rate in uplink, a mobile station, and a radio base station.
2. Description of the Related Art
In a conventional mobile communication system, in an uplink from a mobile station UE to a radio base station Node B, a radio network controller RNC is configured to determine a transmission rate of a dedicated channel, in consideration of radio resources of the radio base station Node B, an interference volume in an uplink, transmission power of the mobile station UE, transmission processing performance of the mobile station UE, a transmission rate required for an upper application, and the like, and to notify the determined transmission rate of the dedicated channel by a message of a layer-3 (Radio Resource Control Layer) to both of the mobile station UE and the radio base station Node B.
Here, the radio network controller RNC is provided at an upper level of the radio base station Node B, and is an apparatus configured to control the radio base station Node B and the mobile station UE.
In general, data communications often cause burst traffic compared with voice communications or TV communications. Therefore, it is preferable that a transmission rate of a channel used for the data communications is changed fast.
However, as shown in FIG. 1, the radio network controller RNC integrally controls a plurality of radio base stations Node B in general. Therefore, in the conventional mobile communication system, there has been a problem that it is difficult to perform fast control for changing of the transmission rate of channel (for example, per approximately 1 through 100 ms), due to processing load, processing delay, or the like.
In addition, in the conventional mobile communication system, there has been also a problem that costs for implementing an apparatus and for operating a network are substantially increased even if the fast control for changing of the transmission rate of the channel can be performed.
Therefore, in the conventional mobile communication system, control for changing of the transmission rate of the channel is generally performed on the order from a few hundred ms to a few seconds.
Accordingly, in the conventional mobile communication system, when burst data transmission is performed as shown in FIG. 2A, the data are transmitted by accepting low-speed, high-delay, and low-transmission efficiency as shown in FIG. 2B, or, as shown in FIG. 2C, by reserving radio resources for high-speed communications to accept that radio bandwidth resources in an unoccupied state and hardware resources in the radio base station Node B are wasted.
It should be noted that both of the above-described radio bandwidth resources and hardware resources are applied to the vertical radio resources in FIGS. 2B and 2C.
Therefore, the 3rd Generation Partnership Project (3GPP) and the 3rd Generation Partnership Project 2 (3GPP2), which are international standardization organizations of the third generation mobile communication system, have discussed a method for controlling radio resources at high speed in a layer-1 and a media access control (MAC) sub-layer (a layer-2) between the radio base station Node B and the mobile station UE, so as to utilize the radio resources effectively. Such discussions or discussed functions will be hereinafter referred to as “Enhanced Uplink (EUL)”.
In the field of the Enhanced Uplink (EUL), as shown in FIG. 3, the mobile station UE is configured to receive an “Absolute Rate Grant Channel (AGCH)” from a serving cell, and to receive a “Relative Rate Grant Channel (RGCH)” from the serving cell and non-serving cells.
Whenever the mobile station UE receives the AGCH, the mobile station UE is configured to transmit an uplink data in a target TTI (Transmission Time Interval) using the transmission rate (or a transmission power offset) which is indicated by the AGCH, irrespective of whether or not to receive of the RGCH.
On the other hand, as shown in FIG. 4, when the mobile station does not receive the AGCH, and detects “UP” command or “DOWN” command in the RGCH, the mobile station UE is configured to increase/decrease the transmission rate (the transmission power offset) in a previous TTI which belongs to the same HARQ process as the target TTI by predetermined value, and to determine the transmission rate (the transmission power offset) in the target TTI.
As shown in FIG. 5, the AGCH is used to increase the transmission rate instantaneously, or the like.
However, when the mobile station UE erroneously detects the RGCH, so as to determine that “UP” command or “DOWN” command is received at the mobile station UE against the instruction of the radio base station Node B, and when the above mentioned method for determining the transmission rate (transmission power ratio) is used, the transmission rate on the TTI prior to the TTI in which the transmission rate was changed instantaneously by the AGCH is increased/decreased. Therefore, the fast transmission rate control using the AGCH cannot be performed.
To be more specific, as shown in FIG. 6, the radio base station Node B transmits the AGCH to the mobile station UE which is transmitting the data at the transmission rate of 100 kbps in t=3 [TTI]. Then, the transmission rate in uplink in the mobile station UE increase up to 1Mbps in t=5 [TTI].
When the mobile station UE erroneously detects “UP” command in the RGCH in t=6 [TTI], the transmission rate is increased by the predetermined value from the transmission rate in t=2 [TTI] which is the previous TTI belongs to the same HARQ process as t=6 [TTI].
In other words, When the mobile station UE erroneously detects “UP” command in the RGCH in t=6 [TTI], the transmission rate is increased by the predetermined value from the transmission rate of 100 kbps in t=2 [TTI].
As a result, the transmission rate, which has been increased up to 1Mbps by the AGCH, decreases rapidly. Therefore, there has been a problem that certain processing such as retransmitting of the AGCH needed to be performed, and a transmission delay occurs.